The use of wind power for producing energy has become increasingly important as petroleum and other fossil fuel costs have risen dramatically during recent years. A national wind energy program has been established to develop necessary technology to economically produce wind energy systems capable of generating significant quantities of electrical power. Large wind turbines of the type for driving 100 kw and larger generators require very long blades of at least 60 feet, and up to 300 feet. Such blades have complex shapes and critical structural requirements. Although lightweight metals including aluminum and the like have been proposed, synthetic resin impregnated glass fiber composite structures offer greater strength to weight characteristics, and offer the potential for low cost, one piece construction, and are thus preferred. It is to the production of such glass fiber structures having high axial stiffness that the present invention is directed.
Processes incorporating resin impregnated glass fiber tape wrapped on mandrels are well known. Nose cone structures often utilize tapes helically wrapped with substantial overlap between tape layers such as disclosed in U.S. Pat. Nos. 3,551,268 and 3,726,751. However, high temperature resistance characteristics are of prime importance and long fiber tapes wrapped for longitudinal axis orientation to optimize axial strength and stiffness requirements are not of primary concern. In U.S. Pat. No. 3,490,983, more complex tapered wingbox beams are given axial strength requirements by machine winding polar wrapped tape layers and hand wrapped tape layers at 45.degree. angles.
Transverse filament tape winding has been proposed for reinforcing plastic pipes as disclosed in U.S. Pat. No. 3,676,246. However, such pipes do not have the complex tapered shapes of the blades and blade spars. Because of this, the proposed tape incorporates only a few locking threads glued to the glass filaments, which tape does not achieve the flexibility and performance characteristics in winding the complex blade and spar structures while achieving critical fiber orientation along the entire structure length according to the present invention. Moreover, the tape is wound on the pipe so that only the tape ends are overlapped unlike that of the present invention.